When a magnetic card is used, holes are punched therein as a means for providing simple visual information to indicate such things as the number of remaining units or the amount of money or the like remaining in prepaid cards, such as telephone cards. These punched holes are used as a means for preventing magnetic cards from being forged. By applying the method of the prior art, the positions of punched holes are checked by optical or magnetic means. Whether forgery or falsification has been made is confirmed by comparing the positions with the contents of the data.
However, in the method of the prior art in which the positions of punched holes are detected optically, detection becomes impossible by merely filling up the punched holes. When detection is performed by a magnetic means, forgery or the like cannot be completely prevented since detection becomes impossible when punched holes are filled up with a material having the same magnetic properties as those of the magnetic cards, for example, scraps produced by punching holes.
The present invention has been accomplished to solve the above-mentioned problems of the prior art.
An object of the present invention is to provide a system for detecting punched holes of magnetic cards, which is capable of detecting the punched holes even if these holes are filled up by the same material as that of the magnetic cards so that the forgery of the magnetic card can be reliably prevented.